Amebiasis is defined as infection with Entamoeba histolytica. While the majority of infections are asymptomatic, intestinal manifestations may include dysentery and colitis. Most amebiasis-associated mortality stems from extra-intestinal infection, which results from invasion of the bowel wall and subsequent spread through the body. See Krogstad, et al. (1978). Amebiasis is one of the world's great health problems, especially in third world countries. It is also a disease of western countries, particularly of travelers, institutionalized persons, and homosexual males.
An amebic infection is usually acquired by the ingestion of food or water contaminated with cysts of Entamoeba histolytica. Sexual transmission has also been reported among homosexual males. Not surprisingly, amebiasis is a common complicating infection in AIDS patients.
At the present time diagnosis of amebiasis usually depends upon recognition of Entamoeba histolytica trophozoites or cysts in stool specimens. Such recognition is technically difficult and time consuming. Thus the test is costly, and unreliable unless run by highly trained technical personnel. Serodiagnostic tests are a valuable supplement to stool smear tests as a means of diagnosing amebiasis, particularly of the more serious invasive infections. The serodiagnostic tests can be run more quickly than the smear tests, and they can be run by less technically trained personnel. Several serodiagnostic tests are now available that can help identify those individuals who have been infected with Entamoeba histolytica. These tests include indirect hemagglutionation, gel diffusion precipitation, and ELISA tests. Unfortunately, all of these serodiagnostic tests share the disadvantage of relying on crude extracts of Entamoeba histolytica as a source of the antigen. The crude extracts of Entamoeba histolytica are really a complex mixture of poorly defined antigens. As a result the individual epitopes and antigenic moieties cannot be identified or produced readily in large amounts. Defined antigens, which can be produced readily in large amounts, are necessary before a more specific serodiagnostic test can be devised. Such a specific serodiagnostic test would make it possible to more accurately detect the presence of antibodies to Entamoeba histolytica in the sera of patients with amebiasis. Thus there is a need for an immunogenic moiety or antigenic reagent that is specific to Entamoeba histolytica and which can be prepared easily in large amounts. It is an object of the present invention to provide an immunogenic compound that will function as a serodiagnostic reagent for amediasis tests. It is a further object of the present invention to provide an immunogenic reagent that is specific to Entamoeba histolytica and which can be prepared easily in large amounts.